New forecasts suggest that Portland will add 123,000 new housing units between 2010 and 2035. Of those, about three-quarters – some 94,000 units – are projected as apartments or condos.

Just 17,000 new units are projected as detached, single-family homes. (Another 12,000 units are expected to be townhouses, duplexes or granny flats built behind existing homes.)

If the projections hold true, Portland will shift from a city of single-family homes to one where apartments are king.

In 2010, about 60 percent of all existing units were single-family homes. But by 2035 — after the dramatic increase in anticipated new apartments — single-family homes would be in the minority, with the share dropping to 47 percent.

Those stats are included in Portland’s “Growth Scenarios Report,” a key analysis tied to city planning and zoning decisions expected to help reshape Portland through 2035. Portland’s Planning and Sustainability Commission is slated to vote on the report in July as part of a city update of its comprehensive plan.

The apartment forecast may seem surprising on its face, but consider: the region promotes dense development through policies that prevent sprawl; Portland is landlocked and doesn’t have new land to plow; Portland is largely built out, leaving limited options for single-family home construction; and more and more Americans nationally are craving urban living.

“The groundwork for this was laid in the 1970s and 80s,” said Tom Armstrong, a supervising planner for Portland. “What’s satisfying … is the market has really responded. The development wouldn’t be happening unless people wanted to live there.”

Armstrong said the official tipping point – with more multi-family construction permits over single-family permits – was within the past five years, and there’s no going back.

As the city redevelops, planners have determined that the smartest way to accommodate new housing and residents is in the central city, along major transit corridors and in designated neighborhood centers with good amenities.

And all those new apartments and homes will help add supply for a growing population.

Portland is projected to add about 260,000 residents between 2010 and 2035, a population increase of nearly 45 percent from the 583,776 tallied in the 2010 Census.

“We can still maintain our livability and make it a nice place to live,” Armstrong said of Portland. “We still have things to work on to get it right.”